The invention relates to improvements in torque applying and indicating apparatus, hereinafter called torque wrenches, and more particularly to instruments for adjusting and calibrating torque wrenches.
Torque wrenches are used for the application of torque to nuts, heads of bolts (particularly bolts with extensible shanks) and like parts, and for simultaneous indication of the magnitude of applied torque. European patent No. 100 023 discloses a torque wrench wherein an elastically deformable arm includes a torque applying portion (e.g., a socket which can receive a nut or the head of a bolt) and a handle which is spaced apart from the torque applying portion and can be engaged by hand to turn the arm about the axis of the nut or bolt in order to apply torque or to reduce the magnitude of applied torque. The torque wrench further comprises a torque indicator having electrical components which serve to ascertain and indicate the magnitude of applied torque. The torque indicator normally comprises one or more strain gages which are affixed to and extend longitudinally of an elastically deformable part of the arm and are connected in one or more Wheatstone bridges or analogous circuits (hereinafter called bridge circuits for short). The signal transmitting output of each bridge circuit is connected with an amplifier which transmits amplified signals to a memory. The latter is connected with a microprocessor by way of an analog-digital converter and includes, or is combined with, digital means for displaying signals denoting the magnitude of applied torque.
In order to calibrate and/or otherwise adjust or test the patented torque wrench, the torque applying portion of the arm is to be connected with a calibrating instrument which is provided with its own torque indicator. Thus, when the arm is used to apply torque to the calibrating instrument, information denoting the magnitude of applied torque is supplied by the indicator of the torque wrench as well as by the indicator of the calibrating instrument. If the information which is furnished by the indicator of the torque wrench departs from that which is furnished by the torque indicator of the calibrating instrument, the electric circuitry of the torque indicator forming part of the torque wrench is adjusted until the information which is furnished by the displaying means of the torque indicator forming part of the wrench matches that which is supplied by the torque indicator of the calibrating instrument. The adjustment involves the utilization of a potentiometer to adjust the aforementioned amplifier or amplifiers which receive signals from the output or outputs of the bridge circuit or circuits in the torque indicator of the wrench. Such adjustment of one or more amplifiers is a time-consuming operation and must be carried out by an experienced operator, especially if the wrench is to be calibrated in a manner to ensure that its indicator can furnish accurate information relating to a rather wide range of torques. Since the torque indicators of many wrenches comprise several bridge circuits, it is then necessary to adjust two or more amplifiers which contributes to complexity and duration of the adjusting and/or calibrating operation. Additional problems arise when the adjustment involves a change from one measuring system to another.